An internal combustion engine of a vehicle operates by energy generated when a mixed gas is combusted in a combustion chamber. The mixed gas includes air and a fuel. An intake air passage, through which the mixed gas or air to be mixed with the fuel is supplied, is connected to a cylinder of the engine. Here, the mixed gas or the air is collectively called intake air of the engine.
A diesel engine includes an exhaust gas recirculation apparatus configured to recirculate exhaust gas which is used as intake air of the engine, thus reducing emission of NOx. An exhaust gas recirculation passage through which the exhaust gas recirculates is connected to the intake air passage. The exhaust gas recirculation passage may include a valve for the recirculated exhaust gas to be selectively supplied to the intake air passage.
The exhaust gas recirculation valve for controlling exhaust gas or a valve housing encasing the valve is exposed to high temperature exhaust gas, thus deteriorating operation performance and durability of the valve. In addition, when the valve and the valve housing made of a material having excellent heat resistance to withstand the high temperature exhaust gas are used, manufacturing costs of the valve and the valve housing excessively increase.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the disclosure, and therefore, it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.